title: Flexibility and dynamics of NhaA Na+/H+-antiporter of Escherichia coli studied by Fourier transform infrared spectroscopy.
abstract: NhaA (41,355Da) is a Na(+)/H(+) antiporter of Escherichia coli which plays a central role in regulation of intracellular pH, cellular Na(+) content, and cell volume [E. Padan, S. Schuldiner, J. Exp. Biol. 196 (1994) 443]. Its activity is strongly regulated by pH and increases over 3 orders of magnitude between pH 7 and 8 [A. Rothman, Y. Gerchman, E. Padan, S. Schuldiner, Biochemistry 36 (1997) 14572]. Protein dynamics and flexibility in the activated and inactivated state, respectively, was analysed by probing accessibility in (1)H/(2)H exchange experiments for the wild type and the mutant G338S which is constitutively active independent of pH [A. Rimon, Y. Gerchman, Z. Kariv, E. Padan, J. Biol. Chem. 273 (1998) 26470]. This was studied by ATR-FTIR difference spectroscopy using a home built microvolume (<5 microl) perfusion chamber [E. Agić, O. Klein, W. Mäntele, Proceedings of the 10th European Conference on the Spectroscopy of Biological Molecules, vol. 93, 2003, ISBN 9634826148; S. Gourion-Arsiquaud, S. Chevance, P. Bouyer, L. Garnier, J.-L. Montillet, A. Bondon, C. Berthomieu, Biochemistry 44 (2005) 8652]. The solution or suspension of the target protein is contained in a chamber with sample volumes of below 5 microl. It is in contact with the ATR crystal and separated from the flowing effector molecules by a dialysis membrane. The flow-ATR unit is characterised by high stability, fast response, and high sensitivity for the IR spectroscopic detection of binding-induced conformational changes and reactions. On the basis of (1)H-(2)H exchange of NhaA followed in the amide I and amide II region of the IR spectrum, it is concluded that the accessible fraction of the polypeptide chain of NhaA increases by more than 10% in the active state. For the mutant, no changes in accessibility were observed for different pH values. The increase of Na(+) concentration increases the extent of exchange. The stability of the wild type protein in the active and inactive form was analysed by measuring the temperature profiles of the IR spectra. A decrease of the structural stability of the protein with activation was observed. Together with the results from (1)H/(2)H exchange, the inactive state represents a more compact form whereas activation induces a more open conformation of the protein.
authors.affiliation: Institut für Biophysik, Johann Wolfgang Goethe-Universität, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main, Germany. maentele@biophysik.uni-frankfurt.de
authors.forename: E
authors.initials: E
authors.lastname: Dzafić
authors.forename: O
authors.initials: O
authors.lastname: Klein
authors.forename: E
authors.initials: E
authors.lastname: Screpanti
authors.forename: C
authors.initials: C
authors.lastname: Hunte
authors.forename: W
authors.initials: W
authors.lastname: Mäntele
mesh_terms: D003903:Deuterium; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D017551:Microdialysis; D050505:Mutant Proteins / Q000737:chemistry; D018583:Pliability; D017433:Protein Structure, Secondary; D011522:Protons; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013997:Time Factors
chemical_list: D029968:Escherichia coli Proteins; D050505:Mutant Proteins; C102839:NhaA protein, E coli; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D003903:Deuterium